Stiffening Member To Increase Fluid Flow Within a Medical Device

ABSTRACT

The present invention relates to a stiffening member, which is a stylet, that helps increase the fluid flow area within a catheter. In a preferred embodiment, the stylet is made of a single piece of flat rectangular stock that can be twisted to provide equal rigidity in all directions. A cross-section of the stylet reveals that the substantially flat rectangular shape of the stylet permits maximum fluid flow between the stylet and the catheter. This results in increased ease in manipulating and removing the stylet from the catheter. In addition, because the preferred embodiment of the stylet comprises a single element, it is easier to manufacture and should result in lower manufacturing costs. Moreover, the use of the present invention should also result in lower overall health-care costs.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to the field of medicaldevices. In particular, this invention pertains to a stylet that helpsincrease the rigidity of a medical device, particularly when the medicaldevice is being inserted.

[0003] 2. Description of Related Art

[0004] Numerous types of catheters are well-known in the prior art; forexample, peripherally inserted central catheters (PICCs) are commonlyused in the prior art. Peripherally inserted central catheters are usedto access the vascular system. In particular, PICCs are used whenlong-term-vascular access is required (e.g., more than two weeksindwelling time in a patient) to avoid multiple injections of thepatient. A PICC is a long catheter that is often inserted mid-way on apatient's arm and the end of the catheter is often placed in thesuperior vena cava of the heart. PICCs often provide access to apatient's vascular system for chemotherapy or other types of intravenousmedication. Because the PICC must often travel through many naturalobstacles in the venous/vascular system, the catheter must be soft andpliable for ease of navigation and to avoid trauma to a blood vessel. Inaddition, the catheter must also be made of bio-compatible materials sothat it will not irritate a patient's veins during the catheter's longdwelling time.

[0005] Unfortunately, PICC lines made of a soft bio-compatible materialare very difficult to insert into a patient because its soft or pliableconstruction causes the PICC to often collapse and bend before enteringthe patient's veins. In order to more quickly and efficiently insert aPICC, a flexible metal stylet (or guidewire) is used as a stiffeningmember inside the catheter during insertion. Once the catheter is placedinside the patient, the guidewire is removed. Guidewires, however, causeseveral problems. There is increased friction between the guidewire andthe inner wall of the catheter since the catheter often makes many turnsand twists before reaching its final destination. As a result, it isoften difficult to manipulate and then remove the guidewire. Second, theuse of the guidewire also introduces the possibility that the guidewiremay perforate a catheter when it is forced against the catheter.

[0006] One solution to these problems is to flush the catheter beforeusing it, during the insertion process to aid manipulation of theguidewire, and/or after the insertion process to assist removal of theguidewire. These flushing solutions often contain heparin and saline.The need for a flushing system and a stiffening member, such as astylet, becomes even more significant as catheters decrease in diameter.A smaller catheter is often more beneficial for patients with small orfragile veins since a smaller catheter causes less trauma to thepatient's veins. The use of smaller catheters has also necessitated thatthe guidewire or stylet be smaller. Yet stylets have not decreased insize to the degree needed. Consequently, the fluid flow area for theflushing solution is decreasing at the same time the need for theflushing solution and a larger fluid flow area are increasing. This iscounter-productive.

[0007] Referring to FIG. 1, a cross-section of a prior art guidewire 102is shown in a small catheter 100 with minimal space for the fluid flowarea 104. In an exemplary catheter with a 0.035 inch diameter, across-sectional area of guidewire 102 occupies about 70% of thecross-sectional area of the lumen of catheter 100. Consequently, onlyabout 30% of the cross-sectional area of catheter's 100 lumen isavailable as the fluid flow area 104. Another prior art embodiment of aguidewire 200 is shown in FIG. 2A. The guidewire 200 is made of threeelements: a flat ribbon of material 207 adjacent to a core 209, both ofwhich are disposed within a twisted-helical coil 205. The resultingfluid flow area 203 between the guidewire 200 and the catheter 201 isminimal.

[0008] A side view of the guidewire 200 of FIG. 2A is illustrated inFIG. 2B. The helical coil 205 is welded on both ends of the ribbon 207at 211 a and 211 b. The twists of the helical coil 205 are often notvisible to the naked eye, but for the sake of clarity, the space betweeneach of the coils in coil 205 have been exaggerated in FIG. 2B. The coil205 often flexes as it twists and turns with the catheter 201. Thisallows some fluid to flow in between the coils 205 and around the core209, which provides stiffness, and the flat ribbon 207. In addition, thecore 209 can also be welded to the flat ribbon 207.

[0009]FIG. 3 illustrates a cross-section of another prior art embodimentin which the guidewire 301 is made of three separate wires 301 a-c,which are braided together. Each wire may have a diameter ofapproximately 0.008 inches while the internal diameter of the catheter300 may be 0.032 inch. FIG. 3 illustrates one disadvantage of the priorart systems. The length of the guidewire cannot be changed withoutaltering or compromising the structural integrity of the guidewire. Forexample, guidewire 301 of FIG. 3 cannot be cut without compromising ordestroying the structural integrity of the guidewire 301 as its threewires 301 a-c will unravel and separate. The same is true for theguidewire 200 of FIG. 2 and its three components, 205, 207 and 209.

[0010] As is evident from FIGS. 1, 2 and 3, the fluid flow area (104,203, 303) around each respective guidewire (102, 200, 301) is severelyrestricted as the diameter of the guidewire approaches the internaldiameter of the catheter. Many prior art guidewires are made of metal sothat the guidewire may not be cut when adjustability of the catheterlength is desired. As a result, in these prior art embodiments, theguidewire is adjusted by first withdrawing the guidewire from theproximal end of the catheter and then cutting the catheter. Thesecatheters thus require extra-tedious manipulations before being able touse them.

[0011] Smaller fluid flow due to decreased area between the guidewire(or stylet) and the inner wall of the catheter is undesirable. Adequatefluid flow is necessary for the flushing solution to aid insertion andremoval of the guidewire (or stylet) in the catheter. In addition,unhindered fluid flow helps prevent friction between the guidewire (orstylet) and the inner wall of the catheter. Thus, it is desirable that aguidewire (or stylet) serves as a stiffening member in a medical device,such as for example, a PICC catheter, during insertion of the medicaldevice. It is also desirable that the shape of the stiffening memberhelps increase fluid flow around the guidewire (or stylet) disposedwithin the medical device.

SUMMARY

[0012] The present invention describes a stiffening member that allowsan increase in the fluid flow area within a medical device, such as acatheter. In one embodiment, the stiffening member is an elongated,substantially rectangular stylet that is disposed within the catheter,such that the stylet can occupy less than half of the lumen area of thecatheter. As a result, adequate fluid flow is allowed between the styletand the inner wall of the catheter. This increases patient comfort. In apreferred embodiment, the stylet is made of substantially flat stocksuch that in cross-section, the longer dimension of the stylet closelyapproximates or is slightly smaller than the internal diameter of thecatheter. Furthermore, in the preferred embodiment, the flat stock istwisted over the length of the stylet to achieve equal rigidity orbendability over the entire length of the stylet in any axis. Differentpitches (i.e., number of twists or turns per inch) may be used to obtainstylets with different degrees of rigidity. Moreover, the pitch within asingle stylet may be varied to create multiple stiffnesses within asingle stylet. For example, the proximal end can have a greater pitchthan the digital end of a stylet to create a softer proximal end. Thisis beneficial since the proximal end is inserted first into the patient.

[0013] The elongated, substantially rectangular stylet comprises themajority of the cross-sectional area of the substantially rectangularstiffening member. Substantially rectangular, as defined, can alsoinclude a cross-sectional area of a single element that is shaped likevarious versions of an I-beam, a dog-bone, an ellipse, an oval, and arectangle. The cross-section of the substantially rectangular stylet hasa long first axis and a short second axis that is not aligned with thefirst axis. The first and second axes, however, are coupled together andare part of a single element stylet.

[0014] The cross-sectional area of the stiffening member is usually suchthat one dimension (the “long” dimension) is at least twice or mostpreferentially, eight times the length of the other dimension (the“short” dimension); in this way, the stiffening member is substantiallyrectangular at least in cross-sectional view. This allows the flushingfluid to flow through at least half of the lumen area within thecatheter, and more preferably through about 80% of the catheter's lumenarea.

[0015] In another embodiment, a cross-sectional area of the elongatedstylet is a percentage up to 65% of a cross-sectional area of thecatheter's lumen. The available fluid flow area is the area not occupiedby the elongated stylet within the catheter's lumen. The cross-sectionalarea of the elongated stylet is formed substantially by a singlestiffening member. In yet another aspect of the present invention, acoating can be placed around the single stiffening member. The coatingdoes not substantially decrease the fluid flow around the stylet.Moreover, the coating can be selected from a group consisting of ahydrogel, or Teflon™, which applies to a tetrafluorethylene fluorocarbonpolymer and a fluorinated ethylene-propylene resin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention is illustrated by way of example and not byway of limitation in the figures of the accompanying drawings in whichlike references indicate similar elements. In addition, for the sake ofclarity, certain elements in a figure may appear larger and are notdrawn to scale.

[0017]FIG. 1 illustrates a prior art guidewire (or stylet).

[0018]FIG. 2A illustrates a prior art guidewire made of threecomponents.

[0019]FIG. 2B is an exaggerated side view of FIG. 2A.

[0020]FIG. 3 illustrates another prior art guidewire that is made ofthree braided wires.

[0021]FIG. 4 illustrates placement of a PICC catheter.

[0022]FIG. 5A illustrates a cross-section of one embodiment of thepresent invention.

[0023]FIG. 5B illustrates a cross-section of a larger embodiment of FIG.5A.

[0024]FIG. 5C illustrates a cross-section of an even larger embodimentof FIG. 5A.

[0025]FIG. 6A illustrates a cross-section of a dog-bone ordumbbell-shaped embodiment of the present invention.

[0026]FIG. 6B illustrates a cross-section of another dog-bone ordumbbell-shaped embodiment of the present invention.

[0027]FIG. 6C illustrates a cross-section of yet another dog-bone ordumbbell-shaped embodiment of the present invention.

[0028]FIG. 7A illustrates another view of the stiffening member 502 ofFIG. 5A.

[0029]FIG. 7B illustrates a side view of another embodiment of thepresent invention.

[0030]FIG. 8 illustrates a cross-section of yet another embodiment ofthe present invention.

[0031]FIG. 9A illustrates a cross-section of an I-beam embodiment of thepresent invention.

[0032]FIG. 9B illustrates a cross-section of another I-beam embodimentof the present invention.

[0033]FIG. 9C illustrates a cross-section of yet another I-beamembodiment of the present invention.

[0034]FIG. 10 illustrates a cross-section of another embodiment of thepresent invention.

DETAILED DESCRIPTION

[0035] An apparatus for enhancing fluid flow within a medical device,such as a catheter is described. In the following description, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout these specific details. In other instances, well-knownstructures may not be shown in order to avoid unnecessarily obscuringthe present invention. In other cases, specific examples are describedand shown in order to thoroughly describe the invention. It will beappreciated that these specific examples are for the purpose ofexplanation and that alternative embodiments will be understood by thosein the art.

[0036] The present invention provides several advantages over the priorart. The present invention increases fluid flow within a catheterwithout sacrificing the mechanical stiffening provided by the stylet.This is especially important in flushable guidewire systems whereunhindered flow of a flushing solution is essential. The flushingsolution helps reduce the friction between the guidewire (or stylet) andthe inner wall of the catheter while the catheter is twisting andturning through the blood vessel. In addition, the flushing solutionaids in manipulating and finally removing the stylet. This reduces thepossibility that the guidewire may become jammed in the catheter andrequire removal of the catheter from the patient. It is also helpful toinfuse fluid through the catheter while advancing the catheter throughthe patient. This is because the fluid dilates the blood vessel andmakes it easier for the catheter to advance, particularly if there is anobstruction in the vessel. Thus, by increasing the area available forfluid flow between the stylet and the inner wall of the catheter, manyof these problems are prevented. Furthermore, increased fluid flowwithin the catheter also increases patient comfort. Moreover, forcatheters with small internal diameters, the present invention allowsmaximum stylet effectiveness while still retaining full flushingcapabilities.

[0037] The present stylet invention may also be easily cut to adjust thelength of the catheter without compromising or destroying the structuralintegrity of the stylet. For example, the structural integrity of theprior art guidewires 200 and 301 of FIGS. 2 and 3 are lost if theguidewires 200 and 301 are cut, because components (205, 207, 209 and301 a-c, respectively) will unravel and separate. This should alsoresult in significant time savings, because unlike the prior art, thestylet of the present invention does not need to be removed before thecatheter is cut. Moreover, the stylet does not need to be presized tofit the exact length of the catheter. Because a physician or a nursecannot usually determine with absolute accuracy the length of catheterneeded for a particular patient, the present invention providesadditional flexibility and time-efficiency to the busy medicalpractitioner. Finally, the present stylet is much easier to manufacturethan prior art examples since it is a single element. For example, theprior art guidewires illustrated in FIG. 3 and in FIG. 2A comprise threeelements. Thus, the present invention should decrease manufacturingcosts and also decrease overall health-care costs.

[0038] One embodiment of the present invention is particularly useful inperipherally inserted central catheters (PICCs), one of which isillustrated in FIG. 4. A PICC 402 is used when long-term-vascular accessis required, for example, more than two weeks, in order to avoidtraumatizing the patient with multiple injections. As shown in FIG. 4, aPICC is a longer catheter that is often inserted midway on a patient'sarm 400 initially and the end of the catheter is often placed in thesuperior vena cava of the heart 401. A PICC must often travel anywherefrom six to twenty inches, depending on the size of the patient, beforeits distal end (the end farthest from the original entry point) reachesits final indwelling point. As a result, a stylet is often used to helpstiffen the catheter, which is often made of a soft bio-compatiblematerial. The soft construction of a catheter often causes the PICC tocollapse and/or bend before entering a patient's veins. Thus, a flexiblemetal stylet enables one to more quickly and efficiently insert a PICC.Since the PICC 402 and thus the stylet, must travel through many naturalbarriers and a fairly long distance through the patient's body, maximumfluid flow between the stylet and the catheter is necessary forincreased patient comfort and decreased incidents of trauma to thepatient's veins.

[0039] Referring to FIG. 5A, a cross-section of one embodiment of thepresent invention is illustrated. A single-elongated, substantiallyrectangular stiffening member 502 is shown within a catheter 500.Substantially rectangular is defined to mean that in cross-section, afirst dimension or first axis 508 of the stiffening member 502 is atleast twice the length of a second dimension or second axis 506 that isperpendicular to the first dimension.

[0040] In particular, first axis 508 is eight-times the length of secondaxis 506. For example, if the internal diameter of catheter 500 is0.035th of an inch and the first axis 508 is about 0.032th of an inchand the second axis 506 is 0.004th of an inch, then stiffening member(in cross-section) occupies about 16.8% of the cross-sectional area ofthe lumen of catheter 500. Thus, a cross-section of the stiffeningmember 502 results in a substantially rectangular shape. It is to beappreciated that other dimensions for first axis 508 and second axis 506can be used within the scope of the present invention. For example,first (or long) axis 508 could be six times longer than second (orshort) axis 506. In addition, first axis 508 provides most of thebending stiffness of elongated stiffening member 502. Bending stiffnessis the force required to bend an object. For example, steel has agreater bending stiffness than rubber. A fluid flow area 504 through atleast more than half of the internal area or lumen of the catheter 500is shown. The fluid flow area 504 is much greater than the prior artfluid flow areas (104, 203 and 303) illustrated in FIGS. 1, 2A and 3,respectively.

[0041] Although stiffening member 502 can operate as a stylet byproviding column strength to the catheter 500 to aid insertion of thecatheter, its substantially rectangular shape (as seen in cross-section)does not greatly reduce the fluid flow like prior art guidewires. In anexemplary embodiment, the stylet has a cross-sectional area that isdefined substantially by the cross-sectional area of the elongated,substantially rectangular stiffening member 502. It will be appreciatedthat an additional treatment, such as a coating (e.g., a hydrogel or aTeflon™ or Teflon™ type material) can be placed around the stiffeningmember 502. The term Teflon™0 applies to tetrafluorethylene fluorocarbonpolymers and fluorinated ethylene-propylene resins. The coating shouldnot substantially increase the diameter or cross-sectional area of thestiffening member 502. Thus, the coating should not dramaticallydecrease fluid flow area 504.

[0042] In FIG. 5A, a cross-section of the flat section of stiffeningmember 502 is shown that is less than the internal diameter of thecatheter 500. It is to be appreciated that the flat section ofstiffening member 502, as shown in crosssection, may also closelyapproximate the internal diameter of catheter 500 in another embodiment.Stiffening member 502 may be made of metal or plastic. It will beapparent to one skilled in the art that stiffening member 502 may bemade of any bio-compatible material that provides column strength tocatheter 500 with minimal irritation to the patient's blood vessel. Itwill also be apparent to one of skill in the art that the presentinvention may also be used in other catheters, such as, a mid-linecatheter and is not restricted to PICCs.

[0043] A cross-section of another embodiment of a stiffening member isshown in FIG. 5B. Stiffening member 510 is disposed within the lumen ofcatheter 500 with a fluid flow area 511. In this particular embodiment,the length of the long axis or first axis of stiffening member 510 isabout four times greater than the length of its short axis or secondaxis. For example, if stiffening member 510 had a first axis of 0.032thof an inch, a second axis of about 0.008th of an inch and the internaldiameter of the catheter is 0.035th of an inch, then the cross-sectionalarea of stiffening member 510 is about 27% of the cross-sectional areaof the lumen for catheter 500. This means that there is a fluid flowarea 511 of about 73% in an embodiment with those dimensions.

[0044] The cross-section of an even larger embodiment of a similarlyshaped stiffening member is illustrated in FIG. 5C. The stiffeningmember 512 is disposed within the lumen of catheter 500. The fluid flowarea 513 of FIG. 5C is less than the fluid flow area 511 of FIG. 5Bbecause the size of the stiffening member has increased. For example, ifthe internal diameter of catheter 500 is 0.035th of an inch, the longaxis or first axis of stiffening member 512 is 0.032th of an inch andthe short axis or second axis of stiffening member 512 is 0.016th of aninch, then stiffening member 512 occupies about 48% of the lumen area ofthe catheter 500 in cross-section. Thus, FIG. 5C illustrates anembodiment where the long axis is about twice the length of the shortaxis. This results in a fluid flow of about 52% of the cross-sectionalarea of the lumen of the catheter 500. The ratio of long axis to shortaxis in the crosssection of the various stiffening members shown inFIGS. 5A-C is meant to be illustrative and not limiting.

[0045] FIGS. 6A-C illustrate a cross-section of a series of differentdog-bone or dumbbell-shaped embodiments for a stiffening member. In allthree figures, FIGS. 6A-C, it will be assumed that the internal diameterof the catheter 600 is 0.035th of an inch for an exemplary catheter. Inaddition, it will also be assumed, for illustrative purposes, that thelong axis (defined like 508 of FIG. 5A)of the stiffening member 602,604, and 608 of each respective figure (FIGS. 6A-C), is 0.032th of aninch.

[0046] In FIG. 6A, for example, the thin middle portion of stiffeningmember 602 can have a thickness of about 0.004th of an inch and the twothicker end portions of stiffening member 602 (which are contiguous tothe middle portion) can be about 0.008th of an inch in an exemplaryembodiment. If one considers the thickness of the end portions to be a“short axis”, in this case 0.008th of an inch, then the “long axis” of0.032th of an inch is four times greater than the short axis. In thisexemplary embodiment, the stiffening member 602, in cross-section,occupies about 16.8% of the cross-sectional area of the lumen ofcatheter 600. Thus, the fluid flow area 603, in this embodiment, isabout 83.2%, which is a significant increase over the prior art.

[0047] Referring to FIG. 6B, the middle portion of stiffening member 604is wider than the middle portion of FIG. 6A, such that thecross-sectional area of stiffening member 604 is increased to about 27%of the cross-sectional area of the lumen of catheter 600. The short axis(defined by the thickness of the two end portions), however, is slightlysmaller than the short axis of FIG. 6A. Consequently, the fluid flowarea 605 has decreased accordingly to about 73% of the cross-sectionalarea of the lumen of catheter 600.

[0048] In yet another embodiment, as illustrated in FIG. 6C, the middleportion and the two end portions of stiffening member 608 are furtherincreased in size. For example, the middle portion can be about 0.012thof an inch and the two end portions (“short axis”) can be about 0.012thof an inch, which means the long axis of 0.032th of an inch is about2.67 times greater than the short axis in this embodiment. According tothese exemplary dimensions, the stiffening member 608 occupies incross-section, about 38.6% of the cross-sectional area of the lumen ofcatheter 600. Thus, the fluid flow area 609 is about 61.4% of thecross-sectional area of the lumen of catheter 600. Thus, FIGS. 6A-Cillustrate how changing the size of the substantially rectangulardumbbell-shaped or dog-bone embodiment of the stiffening member affectsthe resulting fluid flow area. It is to be noted that the fluid flowarea is still greater than the fluid flow area available in prior artFIG. 1, which had a fluid flow area of about 30%.

[0049] Another view of the present invention is illustrated in FIG. 7A.In a preferred embodiment, the stiffening member 700 or stylet is madeof substantially flat rectangular stock that can be twisted to provideequal rigidity or bendability in all directions. Substantially flat, inthis case, is defined to mean without any major curves that will changethe substantially rectangular cross-section of the stiffening member700. It will be apparent to one skilled in the art that the pitch (i.e.,twists or turns per inch) may be varied to change the stiffness of thestylet. In addition, the tip 701 shown in FIG. 7A is narrowed but stillmaintained the same pitch as the rest of the stiffening member 700. Itis to be appreciated that the tip 701 of stiffening member or stylet 700can have different shapes, for example, a flat-shaped tip or a roundedtip. It will also be apparent to one of skill in the art that both endsof the stylet could have, for example, a flat-shaped tip or arotary-swaged rounded tip. The embodiment shown in FIG. 7A is meant tobe illustrative and not limiting.

[0050] A side-view of another embodiment of the present invention isshown in FIG. 7B. A stiffening member 702 having three different pitchesis illustrated. The proximal portion 703 of stiffening member 702 hasthe greatest pitch and is thus, the softest portion of stiffening member702. The distal portion 706 has the smallest pitch and consequently, isthe stiffest portion of stiffening member 702. Mid-section 704 has apitch that is between the pitch of proximal portion 703 and of distalportion 706. Thus, mid-section 704 is stiffer than proximal portion 703,but softer than distal portion 706. It is to be appreciated that anynumber of different pitches can be obtained within a single stiffeningmember 702.

[0051] Referring to FIG. 8, a cross-section of another embodiment of thepresent invention is illustrated. A single elongated, substantiallyrectangular stiffening member 804 is shown within a catheter 800. Inthis embodiment, the substantially rectangular shaped member is anelliptical-shaped member 804 that can be twisted, in one embodiment, toprovide equal rigidity along any axis. The elliptical shape fits within“substantially rectangular” as defined earlier. A cross-section ofelliptical stiffening member 804 has a first axis that is longer than asecond-axis that is perpendicular to the first-axis. In other words, incross-section, the first-axis is the “long” dimension and thesecond-axis is the “short” dimension of substantially rectangularstiffening member 804. The portion of stiffening member 804 that isaligned along the first axis provides most of the mechanical strength.The diameter of the cross-section of the first-axis can closelyapproximate or be less than the diameter of the catheter. Moreover,elliptical stiffening member 804 can be formed so that more than half ofthe lumen area of catheter 800 is available for fluid flow 802.

[0052] A cross-section of stiffening member 804 can also substantiallydefine the cross-sectional area of the stylet. It will be appreciatedthat an additional treatment, such as a coating (e.g., a hydrogel orTeflon™) can be placed around the stiffening member 804. The coatingdoes not substantially increase the diameter or cross-sectional area ofthe stiffening member 804. In other words, the coating should notdramatically decrease fluid flow area 802.

[0053] The pitch of elliptically-shaped stiffening member 804 may bevaried to change the stiffness of the stylet. For example, stiffeningmember 804 can be twisted at one pitch on its proximal end and anotherpitch at its distal end to produce different stiffnesses within a singlestiffening member 804. Furthermore, one end or both ends ofelliptically-shaped member 804 may have many different shapes. Forinstance, one end or both ends can be narrowed to form a tip. The tipcan have different configurations, for example, a flat-shaped tip or arounded tip that can be obtained by a rotary swage. Thus, FIG. 8 ismeant to be illustrative and not limiting.

[0054] FIGS. 9A-C illustrate how the present invention can be defined byhow a cross-sectional area of a stylet is a certain percentage of thecross-sectional area of the catheter's lumen. More specifically, FIGS.9A-C illustrate a cross-section of an I-beam embodiment of the presentinvention relative to the cross-section of the catheter's lumen in whichthe I-beam embodiment is disposed. For example, the internal diameter ofthe catheter 900 can be 0.035th of an inch, and the axis along thelength of the two ends can increase from about 0.012th of an inch inFIG. 9A, to about 0.024th of an inch in FIG. 9B, and then to about0.030th of an inch in FIG. 9C. It is to be appreciated that othervariations of an I-beam are also covered by the present invention. FIGS.9A-C illustrate how the fluid flow area decreases as the cross-sectionalarea of the stiffening member increases from FIGS. 9A-C. In FIG. 9A,stiffening member 902 has a cross-sectional area that is about 18% ofthe cross-sectional area of the lumen of catheter 900. As a result,there is a fluid flow area 903 that is about 82% of the cross-sectionalarea of the lumen of catheter 900.

[0055] As a contrast, in FIG. 9B, the stiffening member 904 is largerand its cross-section occupies about 27.2% of the cross-sectional areaof the lumen of catheter 900. Thus, the fluid flow area 905 is about72.8% of the cross-sectional area of the lumen of catheter 900. In FIG.9C, the ends of the I-beam have increased such that the cross-sectionalarea of the stiffening member 906 has increased to about 38.6% of thecross-sectional area of the lumen of catheter 900. As a result, thefluid flow area 907 is about 62.4% of the cross-sectional area of thelumen of catheter 900, which is still better than the fluid flow area ofthe single-element guidewire in the prior art shown in FIG. 1. It willbe apparent to one skilled in the art that the percentages given forFIGS. 9A-C are illustrative and not meant to be limiting.

[0056] It is to be appreciated that an additional treatment, such as acoating (e.g., a hydrogel or a Teflon™ or a Teflon™-type material) canalso be placed around each of the stiffening members (902, 904, 906)illustrated in FIGS. 9A-C, respectively. This coating should notsubstantially increase the cross-sectional area of the stiffening memberor decrease dramatically the fluid flow area. It will be furtherappreciated that each of the stiffening members (902, 904, 906) shown inFIGS. 9A-C can be twisted and can have varying pitches within a singlestiffening member. Furthermore, although not shown, a stiffening memberthat is shaped like a circular or ellipsoidal O-ring would also fallwithin the scope of the present invention.

[0057] A cross-section of an “X-shaped” or “cross-shaped” embodiment ofthe present invention is illustrated in FIG. 10. An “X-shaped”stiffening member 1004 formed of two substantially rectangular elongatedmembers is disposed within catheter 100 with fluid flow area 1005. Onesubstantially rectangular elongated member has a long axis 1003 that isat least twice the length of its short axis 1006. In addition, thesecond substantially rectangular elongated member also has a long axis1001 that is at least twice the length of its short axis 1002. It is tobe appreciated that long axis 1001 and long axis 1003 and each of theirrespective short axes (1002, 1006) do not have to be equivalent as shownin FIG. 10. For example, long axis 1001 could be shorter than long axis1003 and short axis 1002 could be wider than short axis 1006. It is tobe noted that stiffening member 1004 can be twisted at one pitch orseveral different pitches throughout its entire length. Furthermore, itis also to be appreciated that an additional treatment, such as acoating (e.g., a hydrogel or a Teflon™ or Teflon™-type material) can beplaced around stiffening member 1004. The coating should notsubstantially increase the diameter or cross-sectional area ofstiffening member 1004. Thus, the coating should not greatly decreasethe fluid flow area 1005.

[0058] The foregoing description provides an example of a stiffeningmember, such as a stylet, disposed within a medical device, such as aPICC. It will be apparent to one of skill in the art that the medicaldevice can be, for example, a stent, a cannula, a scope or any otherdevice that uses a stylet or a guidewire. It will be appreciated thatnumerous modifications may be made in practicing the present inventionwithout departing from the spirit and scope of the invention, which isdefined by the following claims.

We claim:
 1. A stiffening member to aid insertion of a medical device,comprising: an elongated member that is disposed within the medicaldevice, wherein said elongated member has a cross-section that issubstantially rectangular.
 2. The stiffening member of claim 1, whereinthe elongated member is twisted.
 3. The stiffening member of claim 2,wherein the medical device has a lumen area and the elongatedsubstantially rectangular member occupies less than half of the lumenarea of the medical device.
 4. The stiffening member of claim 1, whereinthe cross-section of elongated member is selected from a group of shapesconsisting of an oval, a rectangle, an ellipse, an I-beam and a dogbone.
 5. The stiffening member of claim 2, wherein the elongated memberis twisted so that the stiffening member provides equal rigidity in alldirections.
 6. The stiffening member of claim 1, wherein incross-section the elongated member includes a first axis and a secondaxis.
 7. The stiffening member of claim 6, wherein the first-axis islonger than the second-axis.
 8. The stiffening member of claim 7,wherein the first axis provides most of the bending stiffness of theelongated member.
 9. The stiffening member of claim 1, wherein theelongated member has a first end that has a flat-shaped tip.
 10. Thestiffening member of claim 1, wherein the elongated member has a firstend that is rounded.
 11. The stiffening member of claim 7, wherein thefirst and second axes in cross-section are sized to fit within an innerwall of the medical device.
 12. The stiffening member of claim 2,wherein the elongated member can have different pitches along itslength.
 13. A vascular access device, comprising: a catheter having alumen; and an elongated stylet disposed within the lumen, wherein thestylet allows fluid to flow through more than half of the lumen aroundthe stylet.
 14. The vascular access device of claim 13, wherein across-section of the elongated stylet has a substantially flatrectangular shape.
 15. The vascular access device of claim 13, whereinthe elongated stylet is twisted.
 16. The vascular access device of claim15, wherein the elongated stylet is twisted so that the stylet providesequal rigidity in all directions.
 17. The vascular access device ofclaim 15, wherein a pitch (twists per inch) may be varied among astylet.
 18. The vascular access device of claim 15, wherein a pitchwithin the elongated stylet may be varied.
 19. The vascular accessdevice of claim 15, wherein the elongated stylet comprises a materialselected from a group consisting of metal and plastic.
 20. The vascularaccess device of claim 13, wherein a cross-section of a flat section ofthe elongated stylet closely approximates an internal diameter of thecatheter.
 21. The vascular access device of claim 13, wherein across-section of a flat section of the elongated stylet is less than aninternal diameter of the catheter.
 22. The vascular access device ofclaim 13, wherein the elongated stylet has a narrowed tip.
 23. Thevascular access device of claim 13, wherein the elongated stylet has arounded tip.
 24. The vascular access device of claim 13, wherein theelongated stylet includes a coating around a stiffening member, whereinthe stiffening member comprises most of the cross-section of theelongated stylet, and wherein the coating does not substantiallydecrease the fluid flow around the stylet.
 25. The vascular accessdevice of claim 24, wherein the coating is selected from a groupconsisting of a hydrogel, a tetrafluoroethylene fluorocarbon polymer anda fluorinated ethylene-propylene resin.
 26. A vascular access device,comprising: a catheter having a lumen; and an elongated stylet disposedwithin the lumen, wherein a cross-sectional area of the elongated styletis a percentage up to 65% of a cross-sectional area of the lumen, andthe cross-sectional area of the elongated stylet is formed substantiallyby a single stiffening member.
 27. The vascular access device of claim26, wherein the cross-sectional area of the elongated stylet'spercentage is in the range of about 16% to about 50% of thecross-sectional area of the lumen.
 28. The vascular access device ofclaim 26, wherein the elongated stylet is twisted.
 29. The vascularaccess device of claim 28, wherein a pitch within the elongated styletmay be varied.
 30. The vascular access device of claim 26, wherein across-section of a fluid flow area between the cross-section of theelongated stylet and the cross-section of the lumen results in across-sectional fluid flow area of at least 35% of the cross-sectionallumen.
 31. The vascular access device of claim 26, wherein the elongatedstylet can be cut to a predetermined length.